This paper is aimend to explain the constraints on clitic doubling construction in Portuguese, The doubled NP in this construction should be specific, animate and pronominal, Among these constraints, the main discussion of this study goes especially to the pronominal property of the doubled NPs. So far, the reason why the doubled NP satisfies theses constraints has been explained through and hoc rules withous generalization. In this paper. I try to find a generalized explanation explanation of the constraints without inventing construction specific rules. It is proposed in this paper that the doubled NP of clitic doubling construction is adjoined to VP instead of inserting subcategorized NP position. This structure is more favorable to explain stressed semantic interpretation of the NPs. With this clithc doubling structure, the Binding condithion Cis enough th explain why the NPs in question should be pronominal excluding R-expressions or anaphoras from that position, The specific property can be explained by the feature sharing based on the fact that the clitics were historically derived form the deitics. However, any satiisfactory generalized explain is not presented on the animate property of doubled NPs.